Income taxes (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
U.S. federal:
Current	$ (402)	$ 1,651	$ 1,971
Deferred	983	1,189	2,261
Total U.S. federal	581	2,840	4,232
U.S. state and local:
Current	248	327	1,092
Deferred	457	(202)	(1,260)
Total U.S. state and local	705	125	(168)
Reconciliation from U.S. federal statutory tax rate to effective income taxes rate
Federal statutory rate (as a percent)	34.00%	34.00%	34.00%
State and local (as a percent)	(5.70%)	1.10%	(0.70%)
Foreign rate differential (as a percent)	(3.20%)
Stock options (as a percent)	(0.70%)	(2.60%)	1.90%
Non-controlling interests (as a percent)	15.20%	(2.20%)	(2.00%)
Valuation allowance (as a percent)	(119.10%)
Transaction costs (as a percent)	(6.70%)
Purchase price adjustments (as a percent)	6.60%
Revaluation of deferred tax assets (as a percent)	2.80%
Uncertain tax positions (as a percent)	(2.90%)		3.70%
Return to provision (as a percent)	9.30%	(5.30%)	0.20%
Other (as a percent)	1.10%	2.00%	(0.10%)
Income taxes (as a percent)	(69.30%)	27.00%	37.00%
Deferred tax assets:
Net operating loss carryforwards	3,508	1,917
Outside basis differences for U.S. partnerships	2,842	3,289
Stock options	3,018	2,086
Deferred revenue	516	873
Deferred compensation	355	340
State taxes	34	5
Other	404	347
Valuation allowance	(3,963)	(1,669)	(1,822)
Net deferred tax assets	6,714	7,188
Deferred tax liabilities:
Intangible assets	(6,737)	(1,539)
Property and equipment	(2,154)	(189)
Net deferred tax liabilities	(8,891)	(1,728)
Net deferred taxes	(2,177)	5,460
Net operating loss carryforwards
Amount of net operating loss carryforwards	5,847
Release to the valuation allowance	(2,294)	(51)
Foreign loss before income taxes	559	61	45
Period of cumulative results for determination of releasing valuation allowance	3 years
Changes in the valuation allowance
Balance at the beginning of the period	1,669	1,822	3,109
Additions charged to operations	(2,294)	(51)
Decrease credited to operations		(204)	(1,287)
Balance at the end of the period	3,963	1,669	1,822
Windfall tax benefits from stock option exercises	55	2,190	246
United Kingdom
Net operating loss carryforwards
Foreign subsidiary deferred tax asset	644
Brazil
Net operating loss carryforwards
Foreign subsidiary deferred tax asset	69
Federal
Net operating loss carryforwards
Amount of net operating loss carryforwards	20,389	15,283
State
Net operating loss carryforwards
Amount of net operating loss carryforwards	37,153	29,955
Release to the valuation allowance			1,287
Changes in the valuation allowance
Additions charged to operations			1,287
Foreign
Net operating loss carryforwards
Amount of net operating loss carryforwards	$ 3,425	$ 1,588